RESUMEN
Forty children with acute lymphoblastic (33) or myeloid leukaemia (seven) were studied for IgG and IgM antibodies and IgG avidity against human herpesvirus 6 (HHV-6) at the time of diagnosis, and compared with age-, sex- and season-matched children with various neurological diseases of suspected viral origin. Of the children with leukaemia, 97.5% had IgG antibodies and 40% IgM antibodies to HHV-6 compared with 92.3% and 7.7% of reference subjects (P = 0.005). A seronegative child with leukaemia seroconverted 3 weeks after the diagnosis. The avidity of IgG antibodies (based on the resistance to urea treatment) was high in all children with leukaemia. One reference child had HHV-6-specific IgG antibodies with low avidity, which together with his positive IgM indicated an acute infection. The presence of specific IgM antibodies in 40% of children with leukaemia and the high avidity of IgG suggest a reactivation or an inaproppriate primary response to HHV-6 infection. The results support the conclusion of the role of the HHV-6 infection at the onset of childhood leukaemia.